1. Field of the Invention
This invention relates to a rotary head type reproducing apparatus and more particularly to an apparatus arranged to reproduce, with a plurality of rotary heads, an information signal from a record bearing medium which has many recording tracks parallel with the information signal recorded therein and with a plurality of different pilot signals of different frequencies also recorded one by one, in each of the recording tracks.
2. Description of the Prior Art
The rotary head type recording apparatus of the above stated kind include magnetic video recording reproducing apparatus (hereinafter will be called VTR's) which are arranged to perform a reproducing operation by menas of two rotating heads forming oblique recording tracks on a magnetic recording tape, one after another. In this specification, the above stated apparatus will be described by way of example using the VTR.
In carrying out reproduction of a desired record bearing medium moving speed which differs from a speed used for recording (called special reproduction) such as high speed reproduction, low speed reproduction (including still picture reproduction), reverse reproduction, etc. with a rotary head type reproducing apparatus such as a VTR, the reproducing heads must accurately trace one recording track in each scanning field in order to prevent the occurrence of noise bars in order to obtain a reproduced picture which is sharp and stable. In one known method for meeting this requirement, a pattern signal generator is arranged to generate a pattern signal corresponding to a distance from the scanning locus of the reproducing head obtained at a desired tape travel speed to a recording track on the tape. The pattern signal obtained from the pattern signal generator controls some head shifting means such as a piezo-electric conversion element (for example, a bimorph element) which is arranged to shift the reproducing head in a direction perpendicularly crossing the rotation plane thereof.
FIG. 1 is a block diagram showing the conventional VTR of this kind and, particularly, showing the arrangement of parts thereof essentially related to the present invention. In FIG. 1, a magnetic tape 1 is employed as a record bearing medium. Reproducing magnetic heads 2A and 2B have the same azimuth angle and are opposed to each other at 180 degrees. These heads 2A and 2B are mounted on the free ends of piezoelectric conversion elements 3A and 3B, such as bimorph elements operating as shifting means, respectively. The tail ends of the conversion elements 3A and 3B are attached to a rotating member 4. The rotating member 4 is arranged to be rotated by a head rotating motor 5 in the direction of an arrow as shown in the drawing. Although it is not shown in the drawing, the heads 2A and 2B are arranged to be rotated while protruding from a slit provided between a pair of tape guide drums in a known manner. Furthermore, the tape 1 is obliquely lapped more than 180 degrees around this pair of drums. A rotation phase detector 6 is arranged to detect the rotation phase of the heads 2A and 2B and to produce a signal which is used as on a head switching signal (hereinafter referred to as HSW signal). The HSW signal is supplied to a head motor control circuit 7. The head motor control circuit 7 is arranged to control the head rotating motor 5 via a head motor driving circuit 8 on the basis of the output of the detector 6 in such a way as to rotate the heads 2A and 2B at a predetermined rotation phase and at a predetermined rotational frequency. A control signal reproducing head 9 (hereinafter referred to as the CTL head) is arranged to reproduce a control signal (CTL signal) which is recorded on the lower part of the tape 1 at intervals, each corresponding to one frame portion of the signal to be reproduced, in the longitudinal direction of the tape 1. A capstan 10 is arranged to form tape moving means for moving the tape 1 in the longitudinal direction thereof in conjunction with a pinch roller which is not shown. A capstan motor 11 is arranged to rotate the capstan 10. A frequency signal generator 12 is arranged to generate a frequency signal (hereinafter referred to as the capstan FG signal) which is representative of the rotation of the capstan 10. A capstan motor control circuit 13 is arranged to control, via a capstan motor driving circuit 14, the capstan motor 11 on the basis of the CTL signal from the CTL head 9 and the capstan FG signal from the frequency signal generator 12 in such a way as to rotate the capstan 10 at a predetermined phase and at a predetermined rotational frequency. A pattern signal generating circuit 15 is arranged to generate a pattern signal on the basis of the HSW signal from the rotation phase detector 6, the CTL signal from the CTL head 9 and the capstan FG signal from the frequency signal generator 12. The pattern signal is supplied to the piezoelectric conversion elements 3A and 3B for causing the heads 2A and 2B to trace one and the same recording track on the tape 1 in each scanning field in case where reproduction is performed at each of arbitrary varied speeds including still picture reproduction and reverse rotation reproduction among others. A conversion element driving circuit 16 is arranged to drive the conversion elements 3A and 3B based on the pattern signal from the pattern signal generating circuit 15.
FIG. 2 shows, by way of example, the details of the above pattern signal generating circuit 15. The circuit 15 is provided with input terminals 17, 18 and 19 which are arranged to receive the capstan FG signal from the frequency signal generator 12, the CTL signal from the CTL head 9 and the HSW signal from the rotation phase detector 6, respectively. A binary counter 20 is arranged to count the capstan FG signal which is supplied to the terminal 17 which is reset by the CTL signal which is supplied to the terminal 18. A timing signal generating circuit 21 is arranged to generate a timing signal on the basis of and in synchronization with the HSW signal supplied to the terminal 19. A presettable binary counter 22 is arranged to be preset by the timing signal from the timing signal generating circuit 21 with the output of the counter 20 used as a presetting data PD and to count the capstan FG signal supplied to the terminal 17. A digital-to-analog (D/A) converter 23 is arranged to D/A convert the output of the presettable counter 22. A still pattern generator 24 is arranged to generate a still picture reproducing fixed pattern signal on the basis of the timing signal coming from the timing signal generating circuit 21. An adder 25 is arranged to add together the output of the D/A converter 23 and that of the still pattern generator 24. An output terminal 26 is arranged to produce a conversion element controlling pattern signal which is the output of the adder 25.
The special reproducing operation of the VTR which is arranged as mentioned above and, particularly, the operation of the pattern signal generating circuit 15 of FIG. 2 is described with reference to FIGS. 3, 4(A) and 4(B) in the following: In FIG. 3, parts (d)-(g) show the CTL signal, the output of the counter 20 of FIG. 2, the output of the presettable counter 22 or the D/A converter 23 of FIG. 2 and the output of the adder 25 of FIG. 2, respectively, obtained at the time of reproduction performed at a speed increased 1.5 times. FIGS. 4(A) and 4(B) show the scanning center loci of the heads 2A and 2B relative to the center loci of recording tracks on the tape 1 obtained during still picture reproduction and during the 1.5 times increased speed reproduction, respectively.
With the heads 2A and 2B rotated by the head motor 5, the rotation phase detector 6 produces the HSW signal as shown at a part (a) of FIG. 3. Then, the timing signal generating circuit 21 of the pattern signal generating circuit 15 shown in FIG. 2 produces a timing signal which is synchronized with the rise and fall of the HSW signal as shown at a part (b) of FIG. 3. In accordance with this timing signal, the still pattern generator 24 produces a still pattern signal for causing the heads 2A and 2B to be continuously shifted from 0 to -1 track pitch (hereinafter referred to as TP) within a scanning range for one field.
In carrying out a so-called field still reproducing operation in which one field signal recorded in one recording track with a recording head having the same azimuth angle as the reproducing heads 2A and 2B is reproduced alternately by means of the two heads 2A and 2B, the relation of the scanning center loci of the heads 2A and 2B to the recording track on the tape 1 becomes as shown in FIG. 4(A). Referring to FIG. 4(A), full lines represent the center loci of the recording tracks of the field signal recorded by the recording head having the same azimuth angle as the reproducing heads 2A and 2B. Broken lines represent the center loci of recording tracks of a field signal recorded by a recording head having an azimuth angle which differs from that of the heads 2A and 2B. An outline arrow represents the scanning center loci of the heads 2A and 2B. Reference symbol CTL denotes the recording loci of the CTL signal. FIG. 4(B) is also drawn the same manner. As shown in FIG. 4(A), a scanning center loci "c" of the heads 2A and 2B (hereinafter referred to as the head locus "c") become a line segment diagonally connecting the beginning end of a center locus "a" of the track to be reproduced (hereinafter referred to as the track locus "a") to the terminating end of an adjacent track locus "b" on the left side of the track locus "a". To correct this deviation and to adjust the head locus "c" to the track locus "a", the heads 2A and 2B are continuously shifted from 0 to 1 TP within one field scanning range in a direction reverse to the direction in which the tape 1 travels during recording. In other words, assuming that the tape 1 travels in the direction of "+" during recording, the heads 2A and 2B are shifted in the direction of "-".
It will be understood from the above description that the still pattern signal, which is produced from the still pattern generator 24 as shown at the part (c) in FIG. 3, is capable of satisfying the requirement in shifting the heads 2A and 2B for the field still reproduction.
Meanwhile, the capstan FG signal produced from the frequency signal generator 12 with the capstan 10 rotated by the capstan motor 11 is supplied to the counters 20 and 22, which are included in the pattern signal generating circuit 15 of FIG. 2. These counters 20 and 22 count the capstan FG signal. However, since the counter 20 is reset by the CTL signal of the CTL head 9 for every one-frame portion, the upper limit of the counted value of the counter 20 is set at a value corresponding to +2 track pitches. In the event of the 1.5 times increased speed reproduction, since the CTL signal becomes as shown at a part (d) of FIG. 3, the output of the counter 20 becomes as shown at a part (e) of FIG. 3. The presettable counter 22 counts the capstan FG signal while being preset by the timing signal from the timing signal generating circuit 21 (a) part (b) of FIG. 3) at the output value of the counter 20 obtained at that time. Therefore, the count output of the counter 22 or the output of the D/A converter 23 becomes as shown at a part (f) of FIG. 3 during the 1.5 times increased speed reproduction. Accordingly, the adder 25 adds up the output of the D/A converter 23 obtained at that time and the output of the still pattern generator 24 and produces a pattern signal as shown at a part (g) of FIG. 3 during the 1.5 times increased speed reproduction.
Since the counters 20 and 22 are arranged to count the capstan FG signal, the outputs of these counters 20, 22 and the adder 25 include small stepwise variations therein. However, such variations are omitted in the drawing for simplification of illustration.
In the event of 1.5 times increased speed reproduction, the head locus in relation to the track locus on the tape 1 becomes as shown in FIG. 4(B). Referring to FIG. 4(B), reference symbols A1, A2, A3, --- denote head loci of the head 2A; B1, B2, B3, --- denote head loci of the head 2B; and a1, a2, a3, --- denote track loci of the field tracks recorded by a recording head having the same azimuth angle as the heads 2A and 2B. For the first field, the head 2A must be continuously shifted to an extent corresponding to a distance from 0 to +0.5 TP within the first field scanning range in order to adjust the head locus A1 to the track locus a1. For the second field, the head 2B must be continuously shifted to an extent corresponding to a distance from +1.5 TP to +2 TP within the second field scanning range in order to adjust the head locus B1 to the same track locus a1. In the third field, the head 2A must be continuously shifted to an extent corresponding to a distance from +1 TP to +1.5 TP within the third field scanning range in order to adjust the head locus A2 to the track locus a2. In the fourth field, the head 2B must be continuously shifted to an extent corresponding to a distance from +0.5 TP to +1 TP within the fourth field scanning range in order to adjust the head locus B2 to the track locus a3. After that, the above-stated adjustment steps are repeated in a cycle for every four field periods. The pattern signal which is shown at the part (g) in FIG. 3 is appropriate for shifting the heads 2A and 2B in the above-stated manner.
While the 1.5 times increased speed reproducing operation is described by way of example in the foregoing, the pattern signal generating circuit 15 is capable of giving other pattern signals required in controlling the heads 2A and 2B for other reproducing operations to be carried out at desired speeds other than the speed increased 1.5 times.
The pattern signal which is thus obtained from the pattern signal generating circuit 15 is supplied to the conversion element driving circuit 16. Then, the driving circuit 16 drives the piezoelectric conversion elements 3A and 3B to bring the heads 2A and 2B to an applicable reproducing track on the basis of the above-stated pattern signal and the HSW signal from the rotation phase detector 6.
On the other hand, a high density recording tendency of VTR's of recent years calls for tracing the recording tracks with fidelity. To meet this requirement many varied tracking methods have been contrived for accurately correcting the deviation of a reproducing head from the recording tracks (hereinafter referred to as a tracking error). In one of the prior art tracking methods, four pilot signals of different frequencies are superimposed on one-field portions of a video signal one after another during recording. Then, during reproduction, the pilot signals are reproduced from a reproducing track which is mainly traced by a head (hereinafter referred to as the main track) and also from adjacent tracks located on both sides of the main track. Tracking is thus carried out utilizing the pilot signals thus reproduced. In accordance with this method, the tracking error is detected by comparing the levels of the pilot signal components reproduced from the two adjacent tracks.
FIG. 5 shows a situation in which the magnetic tape 1 is arranged to have four kinds of pilot signals recorded thereon. The illustration includes a travelling direction X of the magnetic tape 1; a tracing direction Y of the heads; frequencies f1, f2, f3 and f4 of-the pilot signals; and recording positions of two heads Ar and Br which are indicated by broken lines. As is well known, the two heads Ar, Br rotate at a phase difference of 180 degrees and alternately form recording tracks. One field portion of the video signal is recorded in an area a1 of each track. Each track includes another area a2. While one head Ar or Br forms the track area a1, the other head Ar or Br forms the area a2. The area a2 is formed more or less by VTR's in general. During the recent years, there have been proposed VTR's of the kind arranged to record a digital audio signal by increasing the area a2.
The pilot signal to be recorded in the area a2 of one recording track is identical with the pilot signal which has been recorded in the area a1 of another recording track formed immediately before the track. This is because the pilot signals generated during recording are switched over from one to another at every one field period and are supplied to both of the heads Ar, Br. In other words, while one of the heads Ar or Br is tracing the area a2 the other head Ar or Br is tracing the area a1 which is formed immediately before. Reference symbols Ap and Bp denote the positions of the two heads Ar, Br obtained during a normal reproducing operation.
The technical background mentioned above involves various problems. In the event of the special reproduction to be carried out with the above stated head shifting means, the tracking control with the above stated pilot signals presents a problem: With the head shifting means controlled in the manner as has been described with reference to FIGS. 1-4, the pilot signal which is recorded in the area a2 is not used in forming the pattern signal. Accordingly, no tracking is actually performed until the head Ar, Br reaches the area a1. Thus, any information signal that is recorded in the area a2 cannot be reproduced.
Furthermore, the pattern signal which is formed as shown at the part (g) of FIG. 3 would have a large change in the level every time the heads Ar, Br are switched over from one to another. Therefore, the piezo-electric conversion element A3, B3 would bring about a ringing phenomenon immediately after the switch-over of the heads Ar, Br. Then, the heads Ar, Br become incapable of accurately tracing the recording tracks.
Furthermore, in the case of special reproduction, the pilot signal recorded in the area a2 can hardly be reflected on the tracking control including the formation of a pattern signal. In this case, not all of the recording tracks are reproduced one after another in the same order as the order in which they are recorded. Therefore, when one head Ar or Br is tracing the area a1 and the other head Ar or Br the area a2, the pilot signals recorded in the main tracks being mainly traced by these heads Ar, Br differ from each other. The pilot signals recorded in two adjacent recording tracks naturally differ from each other. Therefore, when the tracking error of the head Ar or Br in the area a1 is detected, it has been hardly possible to detect the tracking error of the other head Ar or Br which is in the area a2. Tracking becomes inaccurate immediately after one of the heads Ar, Br enters the area a1 and thus degrades the reproduced signal of that part.
Furthermore, such a tracking error that arises in special or varied speed reproduction makes it difficult to select a main track. Then, it becomes difficult to discern the kind of pilot signal of the main track. Tracking control by means of pilot signals thus becomes difficult.